W78

The W78 is an American thermonuclear warhead with an estimated yield of 335–350 kilotonnes of TNT (1,400–1,460 TJ), deployed on the LGM-30G Minuteman III intercontinental ballistic missile (ICBM) and housed in the Mark 12A reentry vehicle.

Minuteman III initially carried the older W62 warhead with a yield of 170 kilotonnes of TNT (710 TJ), but starting in December 1979 and ending in February 1982, some W62 were replaced with the W78.

It is thought that the warhead has never been tested at full yield, with the weapon producing a "disappointing" yield shortly before the 1976 Threshold Test Ban Treaty came into force, leading to a redesign of the weapon that was not complete before the treaty came into force.

The dispute was resolved by a panel led by former LLNL director John Foster who found in favor of LANL's yield estimate.

[3] Dimensions of the W78 are unknown, but it fits within the Mark 12A reentry vehicle which is conically shaped.